This application relates in general to a microelectronic interface which is particularly suitable for use in or with nervous systems.
Medical researchers have used electrical current to stimulate action potentials in axons or record such action potentials for many years. Typically, a microelectrode in the form of a needle is inserted into the axon in an animal, for example, and a second electrode is electrically connected to the animal at a distant point from the axon to be stimulated. Such techniques are disadvantageous since the electrical current must pass through a lengthy path through the animal's body. Therefore, the stimulating effect of the current is not localized to the axon so that the current is spread over a large portion of the body. For this reason a large current may be required to generate sufficient current density to have the desired stimulating effect in a particular axon. Such designs are thus wasteful of electrical current. If a large current is used, the useful life of the electrodes is reduced.
In U.S. Pat. No. 4,632,116, Rosen et al. describe a chip perforated with an array of holes for accommodating axons. Each hole contains one or more electrical contacts. The chip is inserted between the severed fascicle ends of the severed nerve so that the proximal axons will propagate through the holes prior to regenerating through paths formed by the degenerated distal axons. Through impulse monitoring, applying blocking potentials and placing selected pairs of proximal and distal contacts in electrical connection, it is stated that nerve impulses from axons in the proximal ends are routed to distal axons in order to restore normal impulse communication and nerve function.
While the chip device described by Rosen et al. in U.S. Pat. No. 4,632,116 marks a significant advance in neuroscience, the performance of the device is nevertheless not entirely satisfactory in many respects. Thus, in U.S. Pat. No. 4,632,116, the electrical contacts employed at the holes are circular or semicircular arcs at the inner surfaces of the holes. The circular or semi-circular arc shaped contacts serve as microelectrodes from which ion flux lines emanate for inducing action potentials in axons. However, when a circular microelectrode is used, the ion flux lines would tend to be diverted from the axon towards other parts of the body where stimulation is not intended. Where a semi-circular shaped pair of microelectrodes are used, the electrical resistance across the insulating gap separating the pair is typically much smaller than the electrical resistance across the axon separating the pair. For this reason, most of the ion flux lines would tend to concentrate in the gaps between the microelectrode and are not effective in inducing action potentials at the axon. Therefore such microelectrodes are not efficient in inducing action potentials in nervous systems. Furthermore, it may be difficult to fabricate tiny neural interfaces where the conducting electrical contacts are at the inner surfaces of the holes in the interface.
In the chip device described by Rosen et al., nerve impulses from axons in the proximal ends are routed to distal axons in order to restore normal impulse communication in nerve function. Thus, Rosen et al. contemplate a one-to-one mapping of nerve impulses so that the nerve impulses from axons in the proximal ends are routed to the distal axons to which they were originally connected before severance in order to restore normal impulse communication and nerve function. Thus Rosen et al. contemplate a one-to-one mapping in the routing of nerve impulses. Since some axons simply will not regenerate, it may not be even possible to route the impulses on a one-to-one basis. Also, it has not been shown that one-to-one mapping is necessary to revive the motor or sensory function of the body. Furthermore, since a nerve fiber can easily contain several thousand axons, the rerouting of the nerve impulses on a one-to-one mapping basis will require an enormous amount of work. It is therefore desirable to provide a more efficient device and method for restoring normal nerve function or for providing a human/machine interface.
It is therefore desirable to provide an microelectronic interface with improved characteristics.